* [CVE-2026-99025][LOW] openvswitch: fix soft lockup in the netlink flow dump
@ 2026-10-26 23:19 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-26 23:19 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99025
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: openvswitch: fix soft lockup in the netlink flow dump
Commit: c995c52eba1926a5e82823fa5573a6f1b1010e5d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c995c52eba1926a5e82823fa5573a6f1b1010e5d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99025
Analysis date: Mon, 26 Oct 2026 19:19:41 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
An Open vSwitch netlink flow dump under sustained softirq load can monopolize a CPU and cause a soft lockup or panic without showing memory corruption or authorization bypass.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99025 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99025
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-99025 LOW https://www.kernelcve.org/list/?q=CVE-2026-99025 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;*CWE-835;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A single Open vSwitch netlink flow dump can monopolize a CPU because ovs_flow_stats_get repeatedly enables BH processing and drains the pending softirq backlog for every emitted flow. Under sustained packet load the backlog can refill while it is being drained, leaving the dumping thread lacking a reschedule point and preventing ksoftirqd or the watchdog stopper thread from running. This can produce a CPU soft lockup and kernel panic, but the code change provides no evidence of UAF, OOB access, information disclosure, or a write primitive. For the CVSS the PR:L in the paranoid vector reflects deployments where OVS administration is delegated to a container root or service account, while the usual host configuration requires CAP_NET_ADMIN. AC:H reflects the need to combine a flow dump with a sufficiently large flow table, sustained softirq pressure, and unfavorable CPU scheduling. The issue is not directly network reachable because traffic can feed the backlog but a local actor must initiate the netlink dump. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 4.7 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE LOCK DEADLOCK DANGER SKB HARDWARE LINUS PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1; no additional technically supported primitive.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable kernel crash / strong DoS: the repeated `spin_unlock_bh()` behavior can make the dump thread continuously process a replenished softirq backlog, causing a CPU soft lockup and possible panic.
* +0 hard-race penalty: several workload conditions are needed, but the production occurrence and sustained-backlog mechanism do not establish a narrow or unreliable race.
* No extra Availability point: CPU lockup and panic are the same availability consequence.
* No memory-corruption, UAF, OOB access, write primitive, disclosure, authorization bypass, or protected-state integrity effect is shown.
* NEW52/B5-R does not apply: there is no heap OOB write, accumulated write index, or later consumption of corrupted structured state.
* NEW53/B3-PENDING and checksum/active-state rules do not apply.
* B4-PENDING does not apply: the patch changes BH scheduling behavior, not an authorization decision.
3. Reachability analysis
A local process must initiate an Open vSwitch netlink flow dump while the datapath has a sufficiently large flow table and the selected CPU receives sustained packet/softirq load. Network traffic can sustain the backlog but does not itself invoke the vulnerable dump.
The supplied diff does not show the generic-netlink capability check or its governing user namespace. The hint suggests CAP_NET_ADMIN is normally required and may sometimes be delegated, but it does not prove either a host-admin-only or complete namespace-scoped trigger. Thus both privilege fields remain UNKNOWN. No special hardware or timing race is required.
4. Primitive and severity reading
The primitive is scheduler/softirq starvation during a bounded flow walk whose nested BH enables absorb an unbounded softirq backlog. The shown outcome is a host CPU soft lockup and possible kernel panic. There is no corrupted object or leverage past denial of service. This is CLASS_C, not an Important-preserving corruption or boundary candidate; automatic downgrade is allowed.
5. One-sentence report phrase
An Open vSwitch netlink flow dump under sustained softirq load can monopolize a CPU and cause a soft lockup or panic without showing memory corruption or authorization bypass.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch supports a workload-dependent availability defect only.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: openvswitch: fix soft lockup in the netlink flow dump
Commit: c995c52eba1926a5e82823fa5573a6f1b1010e5d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c995c52eba1926a5e82823fa5573a6f1b1010e5d
Commit description:
A production compute node carrying a few thousand datapath flows hit a
soft lockup inside a single netlink flow dump and panicked.
ovs_flow_cmd_dump() calls ovs_flow_stats_get() for every flow it
emits, and that releases stats->lock with spin_unlock_bh() once per
CPU that has touched the flow. Every release is a local_bh_enable(),
and each one runs the pending softirq backlog in the dumping thread's
own context.
The skb bounds the flows one callback emits, but not the softirq work
it absorbs. On a CPU that carries the box's packet load the backlog
refills as fast as it drains, so the dumping thread becomes that CPU's
softirq engine. It never sleeps and it has no reschedule point, so
under voluntary preemption nothing can take the CPU away from it:
neither the ksoftirqd the kernel woke to take the work over, nor the
stopper thread the softlockup detector dispatches to refresh its
timestamp.
Hold BH off across the whole callback instead, the way
ctnetlink_dump_table() does, so the nested spin_unlock_bh() stop
draining softirqs. The loop already runs under rcu_read_lock() and
cannot sleep. What it gives up is preemption under CONFIG_PREEMPT,
since a BH-off region is not preemptible outside PREEMPT_RT. The
region stays short: the skb caps the flows one callback emits, and
empty buckets cost no skb space but are each visited once per dump, as
the cursor only moves forward. The table grows on insert and shrinks
only on flush, so the walk is bounded by the largest flow count the
datapath has held. The softirq backlog the callback used to absorb has
no bound at all.
Fixes: 63e7959 ("openvswitch: Per NUMA node flow stats.")
Cc: [email protected]
Signed-off-by: Denis V. Lunev <[email protected]>
Reviewed-by: Ilya Maximets <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/openvswitch/datapath.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c995c52eba1926a5e82823fa5573a6f1b1010e5d
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99025 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99025
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 1
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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